CVE-2022-49093
Estado: ModificadaCrítica (9.8)—
In the Linux kernel, the following vulnerability has been resolved:
skbuff: fix coalescing for page_pool fragment recycling
Fix a use-after-free when using page_pool with page fragments. We encountered this problem during normal RX in the hns3 driver:
(3b) Now while handling TCP, coalesce SKB3 with SKB1:
(3c) Drop SKB2:
Change the logic that checks whether pp_recycle SKBs can be coalesced. We still reject differing pp_recycle between 'from' and 'to' SKBs, but in order to avoid the situation described above, we also reject coalescing when both 'from' and 'to' are pp_recycled and 'from' is cloned.
The new logic allows coalescing a cloned pp_recycle SKB into a page refcounted one, because in this case the release (4) will drop the right reference, the one taken by skb_try_coalesce().
Detalles técnicos trazas, registros y código del informe original
(1) Initially we have three descriptors in the RX queue. The first one
allocates PAGE1 through page_pool, and the other two allocate one
half of PAGE2 each. Page references look like this:
RX_BD1 _______ PAGE1
RX_BD2 _______ PAGE2
RX_BD3 _________/
(2) Handle RX on the first descriptor. Allocate SKB1, eventually added
to the receive queue by tcp_queue_rcv().
(3) Handle RX on the second descriptor. Allocate SKB2 and pass it to
netif_receive_skb():
netif_receive_skb(SKB2)
ip_rcv(SKB2)
SKB3 = skb_clone(SKB2)
SKB2 and SKB3 share a reference to PAGE2 through
skb_shinfo()->dataref. The other ref to PAGE2 is still held by
RX_BD3:
SKB2 ---+- PAGE2
SKB3 __/ /
RX_BD3 _________/
tcp_v4_rcv(SKB3)
tcp_try_coalesce(to=SKB1, from=SKB3) // succeeds
kfree_skb_partial(SKB3)
skb_release_data(SKB3) // drops one dataref
SKB1 _____ PAGE1
\____
SKB2 _____ PAGE2
/
RX_BD3 _________/
In skb_try_coalesce(), __skb_frag_ref() takes a page reference to
PAGE2, where it should instead have increased the page_pool frag
reference, pp_frag_count. Without coalescing, when releasing both
SKB2 and SKB3, a single reference to PAGE2 would be dropped. Now
when releasing SKB1 and SKB2, two references to PAGE2 will be
dropped, resulting in underflow.
af_packet_rcv(SKB2)
consume_skb(SKB2)
skb_release_data(SKB2) // drops second dataref
page_pool_return_skb_page(PAGE2) // drops one pp_frag_count
SKB1 _____ PAGE1
\____
PAGE2
/
RX_BD3 _________/
(4) Userspace calls recvmsg()
Copies SKB1 and releases it. Since SKB3 was coalesced with SKB1, we
release the SKB3 page as well:
tcp_eat_recv_skb(SKB1)
skb_release_data(SKB1)
page_pool_return_skb_page(PAGE1)
page_pool_return_skb_page(PAGE2) // drops second pp_frag_count
(5) PAGE2 is freed, but the third RX descriptor was still using it!
In our case this causes IOMMU faults, but it would silently corrupt
memory if the IOMMU was disabled.CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Puntuación base: 9.8
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.63%
- Percentil entre todas las CVEs puntuadas: 48
- Fecha de la puntuación: 5/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
🎯 Técnicas ATT&CK
Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.
- Explotación
T1190Exploit Public-Facing Applicationinitial access75 % - Impacto principal
T1565.001Stored Data Manipulationimpact80 % - Impacto secundario
T1499.004Application or System Exploitationimpact70 %
CVE crítico (CVSS 9.8 N/A/L) en kernel Linux; use-after-free (CWE-416) explotable remotamente sin autenticación. Impactos: corrupción de memoria de datos (T1565.001) e inamovilidad del sistema (T1499.004) por fallos IOMMU/kernel panic.
Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.
🛡️ Mitigaciones ATT&CK que cubren estas técnicas
Tecnologías afectadas (1)
CWE
- CWE-416
Referencias
JSON original (NVD)
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nskbuff: fix coalescing for page_pool fragment recycling\n\nFix a use-after-free when using page_pool with page fragments. We\nencountered this problem during normal RX in the hns3 driver:\n\n(1) Initially we have three descriptors in the RX queue. The first one\n allocates PAGE1 through page_pool, and the other two allocate one\n half of PAGE2 each. Page references look like this:\n\n RX_BD1 _______ PAGE1\n RX_BD2 _______ PAGE2\n RX_BD3 _________/\n\n(2) Handle RX on the first descriptor. Allocate SKB1, eventually added\n to the receive queue by tcp_queue_rcv().\n\n(3) Handle RX on the second descriptor. Allocate SKB2 and pass it to\n netif_receive_skb():\n\n netif_receive_skb(SKB2)\n ip_rcv(SKB2)\n SKB3 = skb_clone(SKB2)\n\n SKB2 and SKB3 share a reference to PAGE2 through\n skb_shinfo()->dataref. The other ref to PAGE2 is still held by\n RX_BD3:\n\n SKB2 ---+- PAGE2\n SKB3 __/ /\n RX_BD3 _________/\n\n (3b) Now while handling TCP, coalesce SKB3 with SKB1:\n\n tcp_v4_rcv(SKB3)\n tcp_try_coalesce(to=SKB1, from=SKB3) // succeeds\n kfree_skb_partial(SKB3)\n skb_release_data(SKB3) // drops one dataref\n\n SKB1 _____ PAGE1\n \\____\n SKB2 _____ PAGE2\n /\n RX_BD3 _________/\n\n In skb_try_coalesce(), __skb_frag_ref() takes a page reference to\n PAGE2, where it should instead have increased the page_pool frag\n reference, pp_frag_count. Without coalescing, when releasing both\n SKB2 and SKB3, a single reference to PAGE2 would be dropped. Now\n when releasing SKB1 and SKB2, two references to PAGE2 will be\n dropped, resulting in underflow.\n\n (3c) Drop SKB2:\n\n af_packet_rcv(SKB2)\n consume_skb(SKB2)\n skb_release_data(SKB2) // drops second dataref\n page_pool_return_skb_page(PAGE2) // drops one pp_frag_count\n\n SKB1 _____ PAGE1\n \\____\n PAGE2\n /\n RX_BD3 _________/\n\n(4) Userspace calls recvmsg()\n Copies SKB1 and releases it. Since SKB3 was coalesced with SKB1, we\n release the SKB3 page as well:\n\n tcp_eat_recv_skb(SKB1)\n skb_release_data(SKB1)\n page_pool_return_skb_page(PAGE1)\n page_pool_return_skb_page(PAGE2) // drops second pp_frag_count\n\n(5) PAGE2 is freed, but the third RX descriptor was still using it!\n In our case this causes IOMMU faults, but it would silently corrupt\n memory if the IOMMU was disabled.\n\nChange the logic that checks whether pp_recycle SKBs can be coalesced.\nWe still reject differing pp_recycle between 'from' and 'to' SKBs, but\nin order to avoid the situation described above, we also reject\ncoalescing when both 'from' and 'to' are pp_recycled and 'from' is\ncloned.\n\nThe new logic allows coalescing a cloned pp_recycle SKB into a page\nrefcounted one, because in this case the release (4) will drop the right\nreference, the one taken by skb_try_coalesce()."
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"value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: skbuff: corrección de coalescencia para reciclaje de fragmentos de page_pool Corrige un use-after-free al usar page_pool con fragmentos de página. Encontramos este problema durante RX normal en el controlador hns3: (1) Inicialmente tenemos tres descriptores en la cola RX. El primero asigna PAGE1 a través de page_pool, y los otros dos asignan la mitad de PAGE2 cada uno. Las referencias de página se ven así: RX_BD1 _______ PAGE1 RX_BD2 _______ PAGE2 RX_BD3 _________/ (2) Manejar RX en el primer descriptor. Asignar SKB1, eventualmente agregado a la cola de recepción por tcp_queue_rcv(). (3) Manejar RX en el segundo descriptor. Asigne SKB2 y páselo a netif_receive_skb(): netif_receive_skb(SKB2) ip_rcv(SKB2) SKB3 = skb_clone(SKB2) SKB2 y SKB3 comparten una referencia a PAGE2 a través de skb_shinfo()->dataref. La otra referencia a PAGE2 todavía la mantiene RX_BD3: SKB2 ---+- PAGE2 SKB3 __/ / RX_BD3 _________/ (3b) Ahora, mientras maneja TCP, fusione SKB3 con SKB1: tcp_v4_rcv(SKB3) tcp_try_coalesce(to=SKB1, from=SKB3) // tiene éxito kfree_skb_partial(SKB3) skb_release_data(SKB3) // elimina una referencia de datos SKB1 _____ PAGE1 \\____ SKB2 _____ PAGE2 / RX_BD3 _________/ En skb_try_coalesce(), __skb_frag_ref() toma una referencia de página a PAGE2, donde en cambio debería haber aumentado la referencia de fragmento de page_pool, pp_frag_count. Sin la fusión, al liberar SKB2 y SKB3, se eliminaría una única referencia a PAGE2. Ahora, al liberar SKB1 y SKB2, se descartarán dos referencias a PAGE2, lo que provocará un desbordamiento. (3c) Descartar SKB2: af_packet_rcv(SKB2) consume_skb(SKB2) skb_release_data(SKB2) // descarta la segunda referencia de datos page_pool_return_skb_page(PAGE2) // descarta una pp_frag_count SKB1 _____ PAGE1 \\____ PAGE2 / RX_BD3 _________/ (4) El espacio de usuario llama a recvmsg() Copia SKB1 y lo libera. Dado que SKB3 se fusionó con SKB1, también liberamos la página SKB3: tcp_eat_recv_skb(SKB1) skb_release_data(SKB1) page_pool_return_skb_page(PAGE1) page_pool_return_skb_page(PAGE2) // elimina el segundo pp_frag_count (5) PAGE2 se libera, ¡pero el tercer descriptor RX todavía lo estaba usando! En nuestro caso, esto causa fallas de IOMMU, pero corrompería silenciosamente la memoria si IOMMU estuviera deshabilitado. Cambie la lógica que verifica si los SKB pp_recycle se pueden fusionar. Aún rechazamos diferentes pp_recycle entre SKB 'from' y 'to', pero para evitar la situación descrita anteriormente, también rechazamos la fusión cuando tanto 'from' como 'to' son pp_recycled y 'from' es clonado. La nueva lógica permite fusionar un SKB pp_recycle clonado en uno con referencia de página, porque en este caso la versión (4) eliminará la referencia correcta, la tomada por skb_try_coalesce()."
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